In message , at 21:58:02 on Mon, 17
Sep 2012, " remarked:
The first question Tesco ask you is "Have you brought your own bag", at
which point you can put it on the bagging area and it re-calibrates the
weighing scales.

The machines at my local Sainsbury's don't seem to get on with rucksacks
whenever I've tried that. They can cope with normal cloth shopping bags
of the sort I seem to acquire at conferences.

Perhaps because a rucksack might not properly distribute the weight
when placed on the sensor, whereas it's easier with a cloth shopping
bag?

It's possible it's an anti-theft measure, to make sure you don't put
your own bag on the scales with some [un-paid for] items *already* in
it. I might try that next time I'm in Tesco (go in with my own bag but
also a brick or some other item I could not have bought in the store).
--
Roland Perry